The present invention relates to an optical element holding device for holding an optical element, a barrel incorporating the holding device, an exposure apparatus, and a method for manufacturing a device.
FIG. 17 and FIG. 18 show an optical element holding device incorporated in an exposure apparatus, which is used during a lithography step of a manufacturing process for a semiconductor device, a liquid crystal display device, an imaging device, a thin-film magnetic head, a reticle, a photomask, and the like. The conventional optical element holding device includes an annular frame body 302 and three clamp members 306. Three seats (projections) 304 for supporting an optical element 301, such as a lens, are formed at equiangular intervals on the inner circumferential surface of the frame body 302. Three threaded holes 305 are formed in the upper surface of the frame body 302 at positions corresponding to the three seats 304. The clamp members 306 are attached to the threaded holes 305 with bolts 307.
The bolts 307 are fastened to hold the periphery 301a of the optical element 301 between the clamp members 306 and the seats 304.
Due to increasing integration of a semiconductor device, there is a demand for an exposure apparatus enabling exposure of finer patterns. More specifically, there is a demand for an exposure apparatus provided with a projection optical system having an extremely small wave aberration or distortion. To satisfy such a demand, the optical axis of the optical element 301 must be accurately positioned when installing the optical element 301 in the projection optical system.
Conventionally, the optical element 301 is positioned in the following manner. First, the optical element 301 is held on the frame body 302. The outer circumferential surface and the bottom surface of the frame body 302 are then respectively engaged with an inner wall and a receiving portion of a barrel to attach the frame body 302 to the barrel. This positions the optical axis of the optical element 301. The degree of freedom is extremely small and exists when attaching the frame body 302 to the barrel, and the task of attaching the frame body 302 to the barrel is a troublesome task that requires much care.
The optical element 301 is sandwiched between the clamp members 306 and the seats 304 and held by the frame body 302 in a state with subtle degree of freedom. When the frame body 302 is attached to the barrel in a slightly tilted state, the frame body 302 may be subjected to excessive load and may be distorted. When the frame body 302 is distorted, unpredictable stress caused by such distortion may act on the optical element 301 and lower the accuracy of the optical surface of the optical element 301.
A recent exposure apparatus for manufacturing semiconductors uses exposure light of shorter wavelengths to expose finer patterns with high accuracy. For instance, ultraviolet light of an i line (λ=365 nm), far ultraviolet light of a KrF excimer laser (λ=248 nm), ArF excimer laser (λ=193 nm), and F2 laser (λ=157 nm) of short wavelengths are used. In the exposure apparatus using exposure light having a short wavelength as described above, position adjustment of the optical element in the barrel is necessary to maximize the imaging capability with the shorter wavelength of the exposure light. For instance, fine adjustment of the orientation of the optical element 301 in the optical element holding device with respect to the frame body 302 is required.
It is an object of the present invention to provide an optical element holding device facilitating accurate positioning of an optical element, while enabling fine orientation adjustment of the of the optical element. Another object of the present invention is to provide an exposure apparatus that improves the exposure accuracy. A further object of the present invention is to provide a method for manufacturing a device that enables highly integrated devices to be manufactured with high yield.